Just going off the top of my head, but didn't McNally retire 2 years ago, not last year? I'd guess the improvements (assuming they last) would be because our blocking schemes have always called for mobile, athletic linemen, and prior to this year, we mostly had big fat guys.
As for Kollar, every McCargo article I've read has painted Kollar as a major dick. If a coach doesn't click with his players personality-wise, it doesn't matter how good a teacher he is, the message just won't get through. And honestly, this quote from Mark Gaughan's article on Bob Sanders tells me all I need to know:
'"Another thing is just changing your angle," Kelsay said. "You're rushing the quarterback, you're not rushing the offensive tackle. With me last year, I'd be rushing up here and the quarterback would be over there."'
How many times over the past few years have we screamed about Kelsay steaming 8 yards upfield past the QB? Kollar apparently didn't think that was something that needed correcting, but Sanders does. Case closed.